1. Field of the Invention
This invention relates to a color printing technique employing a plurality of inks.
2. Description of the Related Art
In recent years, color ink jet printers have come to enjoy widespread use as image output devices. A typical color ink jet printer employs, in addition to black (K) ink, several kinds of ink of the hues cyan C, magenta M, and yellow Y. Any color in a color image can be reproduced using these several kinds of ink.
In a printer of this kind, ink amounts of each useable ink are determined according to an arbitrary color of the color image. Herein, the process of determining ink amount of each ink used in printing for color reproduction in this manner will be referred to as a “color separation process” or “ink color separation process.” Relationships among color data of a color image and ink amounts of each color are pre-stored in a color conversion look up table (LUT); during printing, ink amounts of each color at each pixel position are determined with reference to the LUT (see, for example, JP10-191089A).
Color reproduction by a particular printer is determined by the particular types of ink useable by the printer. Typically, any color can be reproduced by combining three chromatic primary color inks (e.g., cyan C, magenta M, and yellow Y). In some instances, spot color inks of different hues from these chromatic primary colors ink are used. “Spot color” refers to a color that can be separated into two chromatic primary colors. Where spot color inks are used, the range of color reproduction can be expanded. However, to date, in instances where use of such chromatic primary color inks and spot color inks is possible, no feature has been devised whereby color separation may be performed in consideration of image graininess caused by spot color ink dots, or in consideration of graininess and ink savings.